As usual, the root problem is that workplaces are made of humans. Yes, "culture fit" can absolutely be used to excuse nastiness. It is also a real thing that seriously matters, and ignoring interpersonal dynamics is a very quick way to kill a startup.

I'd just note that you can smuggle nasty behavior into any formal mechanism. Witness the legal system (which you'd engage here) - whining about bad-faith arguments in court is basically a national sport in the US, until the whiner is the plaintiff.